The invention relates to a cost effective and convenient process for the manufacture of fluorinated olefins of the formula RCF.sub.2 CH.dbd.CH.sub.2 where R is C.sub.x Cl.sub.y F.sub.z and y+z=2x+1 which may be used as starting materials for the manufacture of hydrofluorocarbons. The invention is also directed to a practical process for converting these olefins to hydrofluorocarbons via catalyzed fluorination with hydrogen fluoride. The hydrofluorocarbons produced via this process have utility, among other things, as solvents.
Traditionally, chlorofluorocarbons (CFCs) like trichlorofluoromethane (CFC-11), dichlorodifluoromethane (CFC-12) and 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113) have been used as solvents, refrigerants, blowing agents and diluents for gaseous sterilization. These materials, however, are suspect since they are believed to contribute to the stratospheric ozone depletion problem. The fluorocarbon industry has therefore focused its attention on developing stratospherically safer alternatives to these materials. Hydrofluorocarbons (HFC's) like CF.sub.3 CF.sub.2 CH.sub.2 CH.sub.2 F (HFC-356mcfq), which has been identified as a solvent, are candidate replacement materials since they have no ozone depletion potential, contribute negligibly to global warming and offer substantially the same performance advantages such as nonflammability. As a result, methods for the manufacture of these materials need to be developed.
A few methods for the manufacture of compounds of the formula RfCH.dbd.CH.sub.2 where Rf is C.sub.n F.sub.2n+1 are known in the art. See, e.g., U.S. Pat. No. 4,058,573 and Brace et. al., Effect of a perfluoroalkyl group on the elimination and substitution reactions of two homologous series of perfluoroalkyl-substituted iodoalkanes, 49 J. Org. Chem., 2361 (1984). These references disclose the addition of a perfluoroalkyl iodide to ethylene to yield RfCH.sub.2 CH.sub.2 I, followed by dehydroiodination to provide the olefin, RfCH.dbd.CH.sub.2. This method is convenient only for the preparation of small quantities of materials because of the prohibitively high cost of the perfluoroalkyl iodide.
U.S. Pat. Nos. 2,889,379 ('379 patent), 4,798,818 ('818 patent), and 4,465,786 ('786 patent) disclose the preparation of CF.sub.3 CH.dbd.CH.sub.2 by the catalyzed vapor phase fluorination of various halogen-containing C.sub.3 compounds such as CCl.sub.3 CH.sub.2 CH.sub.2 Cl. These references however, do not teach or suggest that higher molecular weight homologs can be prepared by this method.
The halogen exchange in the precursors to the fluorinated olefins of our invention is dissimilar to the halogen exchange reported in these references. That is, the references are replacing the chlorine in a --CCl.sub.3 group with fluorine while we are replacing the chlorine in a --CF.sub.2 CCl.sub.2 CH.sub.2 group with fluorine. U.S. Pat. No. 4,078,007 discloses the liquid phase antimony pentachloride catalyzed fluorination with HF of CCl.sub.3 CH.sub.2 CH.sub.2 Cl (the same compounds used in the '379, '818 and '786 patents) to provide CF.sub.3 CH.sub.2 CH.sub.2 Cl at reaction temperatures of about 85.degree. C. However, the liquid phase antimony pentachloride catalyzed fluorination with HF of CF.sub.3 CCl.sub.2 CH.sub.2 CH.sub.2 Cl (a precursor of the fluorinated olefins of our invention) even at substantially higher reaction temperatures failed to result in even modest fluorination. That is, of the product recovered, 97% was starting material. See Comparative Examples 1 and 2.
As far as methods for the synthesis of HFC's from fluorinated olefins is concerned, Henne et al., Influence of a CF.sub.3 group on an adjacent double bond, 72 J. Am. Chem. Soc., 3369 (1950) report that the CF.sub.3 group in CF.sub.3 CH.dbd.CH.sub.2 adversely affects the rate of addition of acids, HX where X is Br or Cl, to the carbon-carbon double bond. That is, Lewis acid catalysts and elevated temperatures are required to force these additions and even then modest yields and/or conversions may be obtained.
We have discovered: 1) a novel method for the production of fluorinated olefins and 2) a novel method for the manufacture of various HFC's using these fluorinated olefins as starting materials which overcome the drawbacks of the prior art processes discussed above.